This invention relates generally to apparatus for supporting heavy loads in or over a body of water, and more particularly concerns minimizing the rolling motion of a buoyant support for marine drilling, salvage or construction operations. The invention will be described in connection with marine drilling operations, although this is primarily by way of illustration.
Where buoyant members are used to support a derrick and derrick floor for drilling operations over a body of water, it is conventional to mount the derrick and derrick floor on a ship-shaped hull, commonly called a drill ship. The drill ship is typically located at a selected drill site, and usually will be anchored in place by means of a plurality of wire ropes, anchor chains or a combination of wire ropes and anchor chains attached to suitable anchors. These anchoring means are commonly referred to as anchor lines.
The longitudinal axis of the drill ship will normally be oriented as to be parallel to the direction of the prevailing winds as nearly as this can be determined; however, during adverse weather, some component of the wind and wave forces will usually be applied on the drill ship in a direction parallel to the transverse axis of the drill ship. As a result, such component or components of the wind forces and the related wave forces induce rolling motion of the drill ship, about a longitudinal axis thereof. Such rolling motion is detrimental to a drilling operation being conducted due to the relative motion of the ship and pipe or casing extending downwardly into the sea from the vessel, and can indeed be dangerous.